Heretofore in wide use as motor vehicle air conditioner evaporators are those of the so-called stacked plate type which comprise a plurality of flat hollow bodies arranged in parallel and each composed of a pair of dishlike plates facing toward each other and brazed to each other along peripheral edges thereof, and a louvered corrugated fin disposed between and brazed to each adjacent pair of flat hollow bodies. In recent years, however, it has been demanded to provide evaporators further reduced in size and weight and exhibiting higher performance.
To meet such a demand, the present applicant has already proposed an evaporator which comprise a heat exchange core composed of tube groups in the form of two rows arranged in parallel in the front-rear direction and each comprising a plurality of heat exchange tubes arranged at a spacing, a refrigerant inlet-outlet tank disposed at the upper end of the heat exchange core and a refrigerant turn tank disposed at the lower end of the heat exchange core, the refrigerant inlet-outlet tank having its interior divided by a partition into a refrigerant inlet header positioned on the front side and a refrigerant outlet header positioned on the rear side, the inlet header being provided with a refrigerant inlet at one end thereof, the outlet header being provided with a refrigerant outlet at one end thereof alongside the inlet, the refrigerant turn tank having its interior divided by a partition wall into a refrigerant inflow header positioned on the front side and a refrigerant outflow header positioned on the rear side, the partition wall of the refrigerant turn tank having a plurality of refrigerant passing holes formed therein and arranged longitudinally of the wall at a spacing, the heat exchange tubes of the front tube group having upper ends joined to the inlet header, the heat exchange tubes of the rear tube group having upper ends joined to the outlet header, the heat exchange tubes of the front tube group having lower ends joined to the inflow header, the heat exchange tubes of the rear tube group having lower ends joined to the outflow header. The refrigerant flowing into the inlet header of the inlet-outlet tank flows through the heat exchange tubes of the front tube group into the inflow header of the turn tank, then flows into the outflow header through the refrigerant passing holes in the partition wall and further flows into the outlet header of the inlet-outlet tank through the heat exchange tubes of the rear tube group (see the publication of JP-A NO. 2003-75024).
However, the present inventor has conducted extensive research and consequently found that it is difficult to further improve the performance of the evaporator disclosed in the above publication for the reason to be described below.
With the evaporator disclosed in the publication, it is likely that the refrigerant flowing into the inlet header will not dividedly uniformly flow into all the heat exchange tubes connected to the inlet header. As a result, the front heat exchange tube group of the heat exchange core becomes uneven in refrigerant distribution, consequently rendering the refrigerant flowing through the heat exchange tubes of the front group uneven in the distribution of temperatures (qualities of wet vapor) The refrigerant becoming uneven in temperature distribution flows through the inflow header and the outflow header and flows as it is into the heat exchange tubes of the rear group. Thus, the heat exchange tubes in the rear group become uneven in temperature distribution, and the unevenness becomes more pronounced. Accordingly, the air passing through the heat exchange core of the evaporator has varying temperatures at some portions thereof, and the evaporator fails to exhibit fully improved heat exchange performance. This problem becomes aggravated especially when the refrigerant flow rate involves variations or in the case where the flow of air through the heat exchange core varies at some locations.
An object of the present invention is to overcome the above problem and to provide a heat exchanger which is outstanding in heat exchange performance.